1. Field:
This disclosure is concerned generally with containers for blood and blood components and specifically with a container designed to assure fine separation of various components and sub-components of blood.
2. Prior Art:
It is well known that blood can be separated into various components or sub-components which then can be given to patients deficient in one or more components. Major components of whole blood include red blood cells, white blood cells (leucocytes), blood platelets, and plasma and it is well known that the plasma component can be further separated or fractionated into sub-components having therapeutic uses.
Whole blood is commonly collected into a flexible plastic donor bag having connected to it via tubings one or more satellite bags. In a typical situation, whole blood collected in the donor bag is centrifuged, resulting in a lower layer of packed red blood cells and an upper layer of platelet-rich plasma. The platelet-rich plasma may then be expressed via connecting tubing to a satellite bag which, in turn, can be centrifuged to separate the platelets from the plasma which itself may be further fractionated into useful products by known means (e.g. Cohn fractionation).
A blood bag designed to separate newer red blood cells (neocytes) from older red blood cells (gerocytes) has been disclosed recently in U.S. Pat. No. 4,416,778. The bag comprises two separate chambers connected via a conduit with a valve means between the two chambers. There appears no suggestion that the chambers should be in continuous communication or that that type of apparatus would be useful without the intermediate valving means. There are no suggestions of other blood separating applications, especially applications concerned with the separation and use of platelets.
The platelets contained from a single donation represent only a fraction (usually about one-sixth) of the amount used in a common therapeutic administration. Because of this, it is common practice to express the platelets obtained from several satellite bags into a single platelet pooling bag which holds platelets from about six separate donations. Such pooling bags are then used to administer the platelet concentrate to a patient.
When platelets are separated from platelet-rich plasma, it is known that white blood cells (WBC's) are included in the platelet concentrate. The presence of such cells has been associated with febrile transfusion reactions and alloimmunization reactions. See, for example, an article by J. G. Eernisse and A. Brand, Exp. Hemotol., January 1981, Vol. 9, No. 1, pp. 77-83. Although it is not yet a common practice to take steps to separate the WBC's from a platelet concentrate, in those cases where it is done (less than 10%), the platelets of a standard platelet concentrate bag are simply centrifuged and this results in an upper layer of platelets relatively free of WBC's and a lower layer of WBC's. This separation technique removes about 96% of the contaminating WBC's (but at a 21% platelet loss) according to R. H. Herzig et al, Blood, Vol. 46, No. 5, pp. 743-749 (Nov.) 1975. This is thought to be because the interface between the centrifuged platelets and the WBC's is relatively large and, in the ultimate separation of the platelets from the original container, the relatively large interface, in conjunction with the use of a flexible bag, makes it difficult to obtain a fine separation which assures (1) obtaining maximum amount of platelets, and (2) minimum WBC's in the platelet product. In other words, current techniques make it very difficult to obtain a clean cut between the upper platelets and the lower WBC's which occupy the lower volume of a typical platelet pooling bag.
We have now devised a blood bag which avoids the above problems. Unlike the relatively complicated and costly neocyte preparation bags of U.S. Pat. No. 4,416,778, our bag has a fairly simple design and can be used for a variety of separations involving blood components although it is especially suitable as a platelet pooling bag. Details are described below.